1. Field of the Invention
The present invention relates to hard disk drives (HDDs). More particularly, the present invention relates to an adaptive format that takes advantage of the performance capability of different heads that are part of the same HDD.
2. Description of the Related Art
FIG. 1 shows an exemplary high-RPM hard disk drive (HDD) 100 having at least one magnetic read/write head (or a recording slider) 101 and at least one magnetic disk 102. Each magnetic read/write head 101 includes, for example, a tunnel-valve read sensor, that is positioned over a selected track on a magnetic disk 102 using, for example, a two-stage servo system for reading data stored on disk 102. The two-stage servo system includes a voice-coil motor (VCM) 104 for coarse positioning a read/write head suspension 105 and may include a microactuator, or micropositioner, for fine positioning a read/write head 101 over the selected track. As used herein, a microactuator (or a micropositioner) is a small actuator that is placed between a suspension and a slider, and moves the slider relative to the suspension.
Adaptive format techniques are well known for modifying the structure of customer data on each magnetic disk 102 of HDD 100 to compensate for the radial position on each disk and for the bits-per-inch (BPI) performance capability of each head. Nevertheless, the complexity of implementation of conventional adaptive formats has caused only a small percentage of HDDs in the marketplace use an adaptive format technique.
FIG. 2 shows a graph 200 representing the relative BPI of storage as a function of position along the radius of a hard disk for a conventional standard adaptive format. The abscissa of graph 200 is the position along the radius of a disk, with the Inside Diameter (ID) of a disk shown on the left and the Outside Diameter (OD) of the disk shown on the right. The left ordinate of graph 200 is the relative BPI of storage and the right ordinate of graph 200 is the relative data rate in MB/S. Curve 201 represents the data rate as a function of position along the radius of an exemplary hard disk. Because the circumference is greater at the outer diameter of the disk relative to the inner diameter, the data rate at the outer diameter of the disk corresponds to a greater number of bits of data for a single complete revolution of the disk. The data rate and the number of data bits per revolution are reduced in discrete steps represented by curve 201. Curve 202 represents the actual bits per inch as a function of position along the radius of the exemplary hard disk. Curve 202 shows that the actual bits per inch increases as the radius decreases until the number of data bits per revolution steps to a different value, as represented by curve 201. Curve 203 represents what is commonly referred to as the profile of the head BPI capability and is based on curve 202.
FIG. 3 depicts the arrangement of a conventional standard adaptive format on an HDD for four heads, indicated as heads n through n+3. Storage zones 301–303 represent three adjacent portions of hard disks. Storage zone 301 is positioned along the radius of a disk as the closest of the three storage zones to the OD of the disk. Accordingly, storage zone 303 is positioned along the radius of the disk as the closest of the three storage zones to the ID of the disk. Each storage zone 301–303 includes a plurality of tracks 304 and each storage zone 301–303 is separated from each adjacent storage zone by unused or blank tracks 305. As can be seen in FIG. 3, the storage zones for each head changes at the same position in the radius of the hard disk. That is, all of the storage zones are aligned with the tracks and with each other.
Although storage zones 301–303 are each depicted as being about the same size in FIG. 3, it should be understood that the storage zones do not necessarily need to be the same size. For example, storage zone 301 could, for example, correspond to the portion of curve 201 indicated as 204; zone 302 could correspond to the portion of curve 201 indicated as 205; and zone 303 could correspond to the portion of curve 201 indicated as 206. Additionally, while each storage zone shows the tracks associated with four heads grouped together, it should be understood that the tracks associated with each respective head can be physically associated on different hard disks. Further still, while FIGS. 2 and 3 depict a conventional standard format technique on a BPI by head basis, conventional standard adaptive format techniques on a tracks-per-inch (TPI) by head basis are also well-known and can be depicted by both FIGS. 2 and 3.
FIG. 4 shows a graph 400 representing the performance capability distribution of an exemplary plurality of read/write heads with respect to the conventional adaptive format technique represented in FIGS. 2 and 3. Portion 401 of graph 400 represents the portion (a 4 to 5 σ level) of read/write heads that do not have the performance capability to meet the profile represented by curve 203 in FIG. 2. Typically, the mean performance capability 402 of the read/write heads exceeds the performance capability profile.
FIG. 5 shows a graph 500 contrasting the relative BPI performance capability of two exemplary read/write heads, such as heads n and n+1 in FIG. 3, as a function of position along the radius of a hard disk for the standard format technique depicted by FIG. 3. The abscissa of graph 500 is the radius of a disk, with the ID of a disk shown on the left and the OD of the disk shown on the right. The left ordinate of graph 500 is the relative BPI and the right ordinate of graph 500 is the relative data rate in MB/S. Curve 501 represents the data rate as a function of position along the radius of an exemplary hard disk for head n. Curve 503 represents the relative BPI performance capability for head n, which, for this example, has a relatively high BPI performance capability, that is, a performance capability that would be located on the right side of graph 400. Curve 502 represents the data rate as a function of position along the radius of an exemplary hard disk for head n+1. Curve 504 represents the relative BPI performance capability for head n+1, which has a relatively low BPI performance capability, that is, a performance capability that would be located on the left side of graph 400. Because head n is a relatively higher performance head, a portion of curve 503 is at the highest BPI in comparison to curve 504 for head n+1. Nevertheless, because the two heads are part of the same HDD, they are each used to the minimum design BPI performance capability corresponding to curve 400 to the right of portion 401. Moreover, the relatively-higher BPI performance capability of head n is simply not utilized. Curve 505 represents the limit of the bits per inch curve 503 that was conventionally utilized.
One conventional approach to take advantage of the variations in BPI performance capability of different heads is to use a variable-zone-by-head adaptive format technique on a TPI by head or by BPI by head basis. FIG. 6 depicts the arrangement of a conventional variable-zone-by-head adaptive format on an HDD for four heads, indicated as heads n through n+3. Storage zones 601–603 represent three adjacent portions of a hard disk. Storage zone 601 is positioned along the radius of a disk as the closest of the three storage zones to the OD of the disk. Accordingly, storage zone 603 is positioned along the radius of the disk as the closest of the three storage zones to the ID of the disk. Each storage zone 601–603 includes a plurality of tracks 604 and each storage zone 601–603 is separated from each adjacent storage zone by unused or blank tracks 605. Additionally, while each storage zone shows the tracks associated with four heads grouped together, it should be understood that the tracks associated with each respective head are physically associated with different hard disks. Further still, while FIG. 6 depicts a conventional variable-zone-by-head adaptive format technique on a BPI by head basis, conventional variable-zone-by-head adaptive format techniques on a-TPI by head basis are also well-known and can be depicted by FIG. 6.
A conventional variable-zone-by-head adaptive format can be characterized by zones that vary by the BPI performance capability of the corresponding head. For example, as shown in FIG. 6, head n+3 has a higher BPI performance capability than heads n, n+1 and n+2. Thus, storage zone 601 for head n+3 extends less toward the ID of the disk than the corresponding storage zone for each of heads n, n+1 and n+2. As should be readily observable, there is a significant creep in the alignment of the storage zones and the data sectors that can occur with variable-zone-by-head adaptive format that degrades performance. For example, the creep between storage zones 602 and 603, represented by 606, is greater than the creep between storage zones 601 and 602, represented by 607.
Continued market pressures to increase areal densities of HDDs and the slowing of the read/write technology to achieve continued increased areal densities, new adaptive format techniques are needed.
Consequently, what is needed is an adaptive format technique that takes advantage of the performance capability of different heads that are part of the same HDD and that is not utilized by a conventional standard format technique. What is also needed is an adaptive format that does not have the disadvantage of creep exhibited by a conventional variable-zone-by-head adaptive format.